Facet mirror device

ABSTRACT

There is provided a facet mirror device comprising a facet element and a support unit, the support unit supporting the facet element. The support unit comprises a first support element and a second support element, the second support element being connected to the facet element to support the facet element. The first support element is connected to the second support element to support the second support element, the first support element being connected to the second support element via at least one flexure unit, the flexure unit comprising at least one flexure.

BACKGROUND OF THE INVENTION

The invention relates to a facet mirror device that may be used withinan optical device used in exposure processes, in particular inmicrolithography systems. It further relates to an optical imagingarrangement comprising such a facet mirror device. It further relates toa method of supporting a facet element of a facet mirror device and amethod of manufacturing a facet mirror device. The invention may be usedin the context of photolithography processes for fabricatingmicroelectronic devices, in particular semiconductor devices, or in thecontext of fabricating devices, such as masks or reticles, used duringsuch photolithography processes.

Typically, the optical systems used in the context of fabricatingmicroelectronic devices such as semiconductor devices comprise aplurality of optical element modules comprising optical elements, suchas lenses, mirrors, gratings etc., in the light path of the opticalsystem. Those optical elements usually cooperate in an exposure processto illuminate a pattern formed on a mask, reticle or the like and totransfer an image of this pattern onto a substrate such as a wafer. Theoptical elements are usually combined in one or more functionallydistinct optical element groups that may be held within distinct opticalelement units. Facet mirror devices as the ones mentioned above, amongothers may serve to homogenize the illumination light beam (illuminatingthe mask), i.e. to effect a power distribution within the illuminationlight beam which is as uniform as possible.

Due to the ongoing miniaturization of semiconductor devices there is notonly a permanent need for enhanced resolution but also a need forenhanced accuracy of the optical systems used for fabricating thosesemiconductor devices. This accuracy obviously not only has to bepresent initially but has to be maintained over the entire operation ofthe optical system. A particular problem in this context is proper heatremoval from the optical components to avoid uneven thermal expansion ofthese components leading to uneven deformation of these components and,ultimately, to undesired imaging errors.

As a consequence highly sophisticated facet mirror devices have beendeveloped such as they are disclosed, for example, in DE 102 05 425 A1(Holderer et al.) and DE 103 24 796 A1 (Roβ-Meβemer), the respectiveentire disclosure of which is incorporated herein by reference.

Both these documents, among others, show facet mirror devices wherefacet elements with a spherical rear surface sit in an associated recesswithin a support element. The spherical rear surface rests against acorresponding spherical wall of the support element confining thisrecess. While such a sphere to sphere interface theoretically mayprovide a large area of contact with good heat transfer from the facetelement to the support element, this large area contact mainly dependson the manufacturing accuracy of both, the facet element and the supportelement. Furthermore, the spherical recess is rather expensive tomanufacture at an accuracy of a few microns or less as it is desirablein many cases in all three directions in space.

To overcome the problem of heat transfer DE 103 24 796 A1 (Roβ-Meβemer)suggests to place a relatively soft coating (e.g. a gold coating) ontoone of the spherical surfaces which compensates manufacturing tolerancesby deformation. However, despite the low rigidity of this coating, dueto the large contact area such deformation requires relatively largeforces prone to introduce undesired deformation into the facet element.

Another approach is disclosed in DE 102 05 425 A1 (Holderer et al.)wherein the spherical rear surface of the facet element, more or less ina line contact, rests against a conical wall confining the recessreceiving the facet element. This solution, due to the line contactprovides a lower heat transfer while still not considerably reducing themanufacturing effort necessary for the conical wall to have the accuracyneeded for properly positioning the facet element.

A third approach to support the facet elements is disclosed in DE 102 05425 A1 (Holderer et al.) wherein the spherical rear surface of the facetelement, more or less in a three point contact, rests against threesmall spheres each located at a free end of a support pin element. Here,the heat transfer is even worse while as well not considerably reducingthe manufacturing effort necessary for the three small spheres to havethe desired accuracy.

In all three cases outlined above, a manipulating lever is connected tothe rear surface of the facet element, corresponding manipulators actingon the manipulating lever to adjust the position and, predominantly, theorientation of the facet element with respect to the support element.

Furthermore, in some cases, the manipulating lever is used for fixingthe facet element relative to the support element once it has beenadjusted,

SUMMARY OF THE INVENTION

It is thus an object of the invention to, at least to some extent,overcome the above disadvantages and to provide a simple way ofsupporting a facet element of a facet mirror device at a high accuracy,in particular an accuracy of a few microns or less.

It is a further object of the invention to allow easy adjustment andfixation of the facet element to the desired position and orientationwith respect to the support element.

These and other objects are achieved according to the invention which,on the one hand, is based on the teaching that it is possible to providea simple and reliable, easily adjustable support to the facet element ifthe facet element is supported via a flexure unit. Such a flexure unitmay be easily manufactured while providing proper guidance to the facetelement in one or more degrees of freedom allowing easy adjustment ofthe facet element in these degrees of freedom while reliably andprecisely restricting motion in one or more other degrees of freedom.

Thus, according to a first aspect of the invention there is provided afacet mirror device comprising a facet element and a support unit, thesupport unit supporting the facet element. The support unit comprises afirst support element and a second support element, the second supportelement being connected to the facet element to support the facetelement. The first support element is connected to the second supportelement to support the second support element, the first support elementbeing connected to the second support element via at least one flexureunit, the flexure unit comprising at least one flexure.

According to a second aspect of the invention there is provided anoptical imaging arrangement comprising a mask unit adapted to receive apattern, a substrate unit adapted to receive a substrate, anillumination unit adapted to illuminate the pattern, and an opticalprojection unit adapted to transfer an image of the pattern onto thesubstrate. At least one of the illumination unit and the opticalprojection unit comprises a facet mirror device, the facet mirror devicecomprising a facet element and a support unit, the support unitsupporting the facet element. The support unit comprises a first supportelement and a second support element, the second support element beingconnected to the facet element to support the facet element. The firstsupport element is connected to the second support element to supportthe second support element, the first support element being connected tothe second support element via at least one flexure unit, the flexureunit comprising at least one flexure.

According to a third aspect of the invention there is provided a methodof supporting a facet element of a facet mirror device comprisingproviding a facet element and a support element unit and supporting thefacet element via the support unit. The support unit comprises a firstsupport element and a second support element, the second support elementbeing connected to the facet element to support the facet element. Thefirst support element is connected to the second support element tosupport the second support element, the first support element beingconnected to the second support element via at least one flexure unit,the flexure unit comprising at least one flexure.

According to a fourth aspect of the invention there is provided a methodof manufacturing a facet mirror device comprising, in a preparationstep, providing a facet element and a support unit, the support unitcomprising a first support element and a second support element, thefirst support element, to support the second support element, beingconnected to the second support element via at least one flexure unit,the flexure unit comprising at least one flexure; and, in a supportingstep, connecting the facet element to the second support element tosupport the facet element via the support unit.

Further aspects and embodiments of the invention will become apparentfrom the dependent claims and the following description of preferredembodiments which refers to the appended figures. All combinations ofthe features disclosed, whether explicitly recited in the claims or not,are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a preferred embodiment of anoptical imaging arrangement according to the invention which comprises apreferred embodiment of a facet mirror device according to the inventionand with which preferred embodiments of methods according to theinvention may be executed;

FIG. 2 is a schematic top view of the facet mirror device of FIG. 1;

FIG. 3 is a schematic sectional representation of a part of the facetmirror device of FIGS. 1 and 2 (along line of FIG. 2);

FIG. 4 is a block diagram of a preferred embodiment of a method ofmanufacturing a facet mirror device comprising a preferred embodiment ofa method of supporting the facet element according to the inventionwhich may be used for the optical imaging arrangement of FIG. 1.

FIG. 5 is a schematic sectional representation of a detail of a furtherpreferred embodiment of a facet mirror device according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

In the following, a first preferred embodiment of an optical imagingarrangement 101 according to the invention will be described withreference to FIGS. 1 to 3. In order to facilitate the explanations givenbelow an x,y,z-coordinate system has been introduced into the Figuresand will be used throughout the following description. In the following,the z-direction designates the vertical direction. However, it will beappreciated that, with other embodiments of the invention, any otherorientation in space of this x,y,z-coordinate system and the componentsof the optical imaging arrangement, respectively, may be chosen.

FIG. 1 is a schematic and not-to-scale representation of the opticalimaging arrangement in the form of an optical exposure apparatus 101used in a microlithography process during manufacture of semiconductordevices. The optical exposure apparatus 101 comprises an illuminationunit 102 and an optical projection unit 103 adapted to transfer, in anexposure process, an image of a pattern formed on a mask 104.1 of a maskunit 104 onto a substrate 105.1 of a substrate unit 105. To this end,the illumination unit 102 illuminates the mask 104.1. The opticalprojection unit 103 receives the light coming from the mask 104.1 andprojects the image of the pattern formed on the mask 104.1 onto thesubstrate 105.1, e.g. a wafer or the like.

The illumination unit 102 comprises an optical element system 106 (onlyshown in a highly simplified manner in FIG. 1) including a plurality ofoptical element units such as optical element unit 106.1. As will beexplained in further detail below, the optical element unit 106.1 isformed as a preferred embodiment of a facet mirror device according tothe invention. The optical projection unit 103 comprises a furtheroptical element system 107 including a plurality of optical elementunits 107.1. The optical element units of the optical element systems106 and 107 are aligned along a folded optical axis 101.1 of the opticalexposure apparatus 101.

In the embodiment shown, the optical exposure apparatus 101 operatesusing light in the EUV range at a wavelength between 5 nm to 20 nm, moreprecisely at a wavelength of 13 nm. Thus, the optical elements usedwithin the illumination unit 102 and the optical projection unit 103 areexclusively reflective optical elements. However, it will be appreciatedthat, with other embodiments of the invention working at differentwavelengths, any type of optical elements (refractive, reflective ordiffractive) may be used alone or in an arbitrary combination. Theoptical element system 107 may comprise a further facet mirror deviceaccording to the invention.

As can be seen from FIGS. 2 and 3, the facet mirror device 106.1comprises a support unit 108 supporting a plurality of facet elements109 (only one of which is shown in FIG. 3). In the embodiment shown 900facet elements 109 are supported on the support unit 108. However, itwill be appreciated that, with other embodiments of the invention, atany other number of facet elements 109 may be carried by the supportunit 108. For example, with certain preferred embodiments of theinvention, up to 2000 facet elements 109 or even more are supported onthe support unit 108. It should be noted that, preferably, as many facetelements 109 as possible are supported on the support unit 108 to obtainhomogenization of the illumination light. Numbers of up to 4000 facetelements 109, more preferably, up to 16000 facet elements 109, may berealized.

In the embodiment shown, the facet elements 109 are arranged such that asmall gap of less than 0.05 mm is left between them. Hence, as can beseen in particular from FIG. 2, a regular rectangular matrix of facetelements 109 is formed on the support unit 108 providing a minimumamount of loss in radiant power. However, it will be appreciated that,with other embodiments of the invention, any other arrangement of facetelements may be chosen according to the optical needs of the imagingdevice, the facet mirror device is used for.

As can be further seen from FIGS. 2 and 3, in particular from FIG. 2,each facet element 109, in a top view (along the z-direction), as anouter contour of substantially rectangular shape, more precisely ofsubstantially squared shape. However, with other embodiments of theinvention, any other geometry of this outer contour may be chosen suchas, for example, an arbitrarily curved outer contour, a circular outercontour, an elliptic outer contour, a polygonal outer contour orarbitrary combinations thereof.

In the embodiment shown, each facet element has a concave front surface109.1, a planar rear surface 109.2 and a lateral surface 109.3. Thefront surface 109.1 is a reflective surface optically used duringoperation of the optical imaging arrangement 101 in order to providehomogenization of the illumination light provided by the illuminationunit 102. The reflective surface 109.1 may be provided via a reflectivecoating applied to the front surface 109.1 which is adapted to thewavelength of the illumination light used (typically, in order toprovide maximum reflectivity at the respective wavelength). With certainembodiments of the invention a reflective grating may be provided at thefront surface of the facet elements.

In the embodiment shown, the front surface 109.1 is a spherical surface.However, it will be appreciated that, with other embodiments of theinvention, any other shape of the front surface may be chosen dependingon the optical task to be performed by the facet mirror device. Hence,apart from such spherical surfaces, aspherical as well as planarsurfaces as well as arbitrary combinations thereof may be used.Furthermore, convex front surfaces may also be used.

Furthermore, it should be noted that the optically usable front surface109.1 of the facet element 109 may be of any suitable size. Preferably,the size of the front surface 109.1 ranges from 10 mm² to 400 mm², inparticular from 50 mm² to 150 mm², more preferably from 90 mm² to 110mm².

The support unit 108 comprises a first support element in the form of abase plate 108.1. Each facet element 109 has an associated secondsupport element 108.2 which, in the embodiment shown, is a substantiallypin-shaped body inserted into and reaching through an opening 108.3within the base plate 108.1. In the embodiment shown, the opening 108.3is a cylindrical bore. However, any other geometry may be chosen forthis recess 108.3 within the base plate 108.1. Furthermore, in theembodiment shown, the base plate 108.1 is a planar element. However,depending e.g. on the optical requirements, an arbitrary geometry (e.g.an at least section wise curved geometry) may be chosen for the baseplate.

One end of the second support element 108.2 is connected to the rearside 109.2 of the facet element 109 to support the latter. The secondsupport element 108.2, in turn, is connected to the first supportelement 108.1 via a flexure unit 108.4 to support the second supportelement 108.2 and, consequently, the facet element 109 on the firstsupport element 108.1.

The flexure unit 108.4 is located at the front side of the first supportelement 108.1 facing towards the facet element 109. The flexure unit108.4 comprises a plurality of flexures in the form of leaf springelements 108.5 connected at their ends to the second support element108.2 and a ring-shaped linking section 108.6, respectively.

In the embodiment shown, four leaf spring elements 108.5 are evenlydistributed at the circumference of the second support element 108.2.However, it will be appreciated that, with other embodiments of theinvention, any other number of leaf spring elements or flexures may beprovided. In particular, one single leaf spring element may also beprovided connecting the linking section and the second support elementin the manner of a continuous membrane extending over substantially theentire circumference of the second support element.

In the embodiment shown, each leaf spring element 108.5, in a top view(along the z-axis) is a substantially rectangular element. Thetransverse dimension of the leaf spring element 108.5 is selected suchthat (at the interface with the second support element 108.2) it extendsover about 15% of the circumference of the second support element 108.2.However, it will be appreciated that, with other embodiments of theinvention, any other suitable shape and dimensions may be selected forthe leaf spring elements.

As can be seen from FIG. 3, the leaf spring elements 108.5 are formedmonolithic with the second support element 108.2 and the linking section108.6, while the linking section 108.6 is connected to the first supportelement 108.1 by any suitable connection (not shown in greater detail)such as a positive connection, a frictional connection, an adhesiveconnection or arbitrary combinations thereof. However, it will beappreciated that, with other embodiments of the invention, the linkingsection may also be formed monolithic with the first support element.The same applies the other way round two the connection between the leafspring elements and the second support element.

The second support element 108.2 protrudes from the rear side of thefirst support element 108.1 facing away from the facet element 109.Here, in the mounted state (shown in FIG. 3), the first support element108.1 and the second support element 108.2 are substantially rigidlyconnected via a connector element in the form of a connector plate108.7. The connector plate 108.7 is locking the first support element108.1 and the second support element 108.2 in their mutual relativeposition and orientation. Hence, the connector plate 108.7 also takespart in supporting the facet element 109.

The connector plate 108.7 is connected to the first support element108.1 and the second support element 108.2 by any suitable connectionsuch as a positive connection, a frictional connection, an adhesiveconnection or arbitrary combinations thereof. Preferably, the respectiveconnection is formed by an adhesive connection such as by gluing,soldering or welding as it indicated by the contours 110, 111 and 112.

As will be explained now in greater detail with reference to FIGS. 2 to4 the facet mirror device 106.1 is manufactured according to a preferredembodiment of the method according to invention using a preferredembodiment of the method of supporting a facet element according to theinvention.

According to FIG. 4, in a preparation step 113.1, the components of thesupport unit 108 and the facet elements 109 are manufactured as it hasbeen outlined above. In the embodiment shown, the facet elements aremade of silicon (Si), while the support element is made of siliconcarbide (SiC). With such a material pairing and beneficial heat transferfrom the facet elements 109 (typically reaching temperatures of 100° C.to 150° C. during operation of the imaging arrangement 101) may beobtained.

However, it will be appreciated that, with other embodiments of theinvention, the facet element may be made of silicon carbide (SiC),quartz (SiO₂), silicon aluminium (SiAl) Zerodur® (a glass ceramic asmanufactured by SCHOTT AG, Mainz, DE), ULE™ (ultra low expansiontitanium silicate glass as manufactured by Corning Incorporated,Corning, N.Y. 14831, USA), other glass ceramics as well as copper (Cu)or aluminium (Al) coated with N1P or MoSi layers; while the supportelement may be made of stainless steel, copper (Cu), aluminium (Al),reaction bonded silicon infiltrated silicon carbide (SiSiC), Zerodur® orother glass ceramics. It should be noted that, preferably, a matching ofthe coefficient of thermal expansion (CTE) is provided for the facetelement and the support element.

Then, in a connecting step 113.3 of a supporting step 113.2, the secondsupport element 108.2 is introduced into the opening 108.3 until thelinking section 108.4 rest against the run-on surface of the firstsupport element 108.1. Subsequently, the linking section 108.4 isconnected to the first support element 108.1 as it has been outlinedabove.

Then, the facet element 109 is connected to the second support element108.2 by any suitable connection (not shown in greater detail) such as apositive connection, a frictional connection, an adhesive connection orarbitrary combinations thereof. However, it will be appreciated that,with other embodiments of intervention, the facet element 109 may beconnected to the second support element 108.2 prior to connecting thelatter to the first support element 108.1.

Then, in an adjustment step 113.4 of the supporting step 113.2, theposition and orientation of the facet element 109 with respect to thefirst support element 108 is adjusted according to the opticalrequirements for the facet mirror device 106.1 during later operation inthe imaging arrangement 101.

To this end, an adjustment device in the form of a manipulator 114controlled by a control device 115 is used to generate a correspondingadjustment force on an adjustment interface 108.8 of the second supportelement 108.2 as it is shown in FIG. 3. Under the control of the controldevice 115 a relative motion may be generated between the manipulator114 and the facet mirror device 106.1 is such that the manipulationforce F generated may induce the appropriate adjustment motion toprovide proper adjustment of the latter.

It will be appreciated that the leaf spring elements 108.5 of theflexure unit 108.4 provide guidance to the second support element 108.2and facet element 109 by restricting relative motion in twotranslational degrees of freedom (namely the x- and y-direction) and onerotational degree of freedom (namely rotation about the z-axis) whileallowing orientation adjustment in two rotational degrees of freedom(namely rotation about the x- and y-axis) and position adjustment in onetranslational degree of freedom (namely the z-direction). Hence, in avery simple manner, proper height and inclination adjustment of thefacet element 109 may be achieved.

It will be further appreciated that, with certain embodiments of theinvention, the manipulator 114 may also be used to adjust the rotationof the facet element 109 (then already mounted to the second supportelement 108.2) about the z-axis prior to connecting the linking section108.4 of the second support element 108.2 to the first support element108.1.

Assessment of the adjustment of the optically used front surface 109.1is performed using the measurement results of a measurement device 116.In the present embodiment, the measurement device 116 is an opticaldevice comprising an emitter 116.1 emitting a measurement light beam116.2 towards the front surface 109.1. The measurement light beam 116.2is reflected at the front surface 109.1 and reaches a sensor 116.3 ofthe measurement device 116.

In the embodiment shown, the emitter is a conventional emitter usingmeasurement light at a wavelength of 633 nm. Hence, it may be necessaryto provide a measurement section at the front surface 109.1 having areflective coating adapted to this wavelength of the measurement light(provided that the reflective coating of the front surface 109.1 adaptedto the exposure light does not provide sufficient reflection at themeasurement light wavelength). However, it will be appreciated that,with other embodiments of the invention, other wavelengths may be usedfor the measurement light, such that, eventually, no such additionalmeasurement section may be necessary.

The signals of the sensor 116.3 are forwarded to the control device 115which, in turn, performs the assessment of the adjustment of the frontsurface 109.1 using these signals. It will be appreciated that thecontrol device 115, as a function of the signals of the sensor 116.3,controls the manipulator 114 to provide rapid proper adjustment of thefront surface 109.1.

It will be appreciated that, in the embodiment shown, the front surface109.1 is adjusted at an angular accuracy of less than 100 μrad. However,it will be appreciated that, with other embodiments of the invention,depending on the optical requirements during later operation of theimaging arrangement 101, any other angular accuracy may be chosen.

Once the adjustment of the facet element 109 is completed, in a facetfixation step 113.5 of the supporting step 113.2, the facet element 109is fixed in place by connecting the connector plate 108.7 to the secondsupport element 108.2 as it has been outlined above.

In the present example, a laser welding technique is used to provide thefixed adhesive connection 112 between the connector plate 108.7 and thesecond support element 108.2. However, it will be appreciated that, withother embodiments of the invention, apart from the laser weldingtechnique as outlined above, any other suitable bonding technique (suchas e.g. fusion bonding, gluing, clamping etc.) may be used alone or inarbitrary combination to provide proper connection and relative fixationbetween the facet elements and the support unit. Such suitable bondingtechniques include, for example, gluing, soldering, laser soldering,welding, diffusion bonding etc.

The connector plate 108.7 had been connected to the first supportelement 108.1 prior to the adjustment step. However, it will beappreciated that, with other embodiments of the invention, theconnection between the connector plate 108.7 and the first supportelement 108.1 may also be applied at any point in time during or afterthe adjustment of the facet element as it has been outlined above.

Once the facet fixation step 113.5 is completed, the manipulator 114disengages the adjustment interface 108.8 of the second support element108.2 as it is indicated by the dashed contour in FIG. 3.

In a step 113.6 it is then checked if a further facet element 109 is tobe mounted to the support element 108. If this is the case the methodjumps back to step 113.3 for executing the supporting step for the nextfacet element 109 to be mounted. Otherwise, the method ends in step113.7.

Heat removal from the facet mirror device 106.1 during operation of theimaging arrangement 101 may be achieved using a cooling mediumcirculating through cooling channels as they are indicated by the dashedcontours 117 (see FIG. 3).

The connection between the first support element 108.1 and the secondsupport element 208.2 may be made in a sealing manner such that, duringoperation of the facet mirror device 106.1, the rear side of the basebody 108 (facing away from the facet elements 109) may be cooled by afluid, e.g. a cooling medium, while the space surrounding the facetelements 109 is evacuated (or, depending on the wavelength of theillumination light, eventually filled with a gas). This may be achievedin a particularly simple manner in specific embodiments where one singleleaf spring element is provided connecting the linking section and thesecond support element in the manner of a continuous membrane extendingover the entire circumference of the second support element as it hasbeen described above.

In the embodiment shown, the flexure unit comprises flexure is in theform of a leaf spring elements. However, it will be appreciated that,with other embodiments of the invention, other types of flexure is maybeused. For example, instead of a leaf spring element, configuration maybe used comprising two elastic hinges each formed at one end of a lessflexible section. For example, the leaf springs 108.5 could be replacedby such a configuration, one elastic hinge being formed at thetransition to the linking section 108.6 and the other elastic hingebeing formed at the transition to the second support element 108.2.

Second Embodiment

In the following, a second embodiment of the facet mirror device 206.1according to the invention will be described with reference to FIG. 5.The facet mirror device 206.1 in its basic design and functionalitylargely corresponds to the facet mirror device 106.1 and may replace thefacet mirror device 106.1 in the optical imaging device 101 of FIG. 1.In particular, the method of supporting a facet element and the methodof manufacturing the facet mirror device as they have been describedabove in relation to the first embodiment (FIG. 4) may be executed aswell in the context of this facet mirror device 206.1. Thus, it is heremainly referred to the explanations given above and only the differenceswith respect to the facet mirror device 106.1 will be explained infurther detail. In particular, similar parts are given the samereference numeral raised by the amount 100 and (unless explicitlydescribed in the following) in respect to these parts reference is madeto the explanations given above in the context of the first embodiment.For example, elements 209.1, 209.2, 217, 209.3, 208.3 and 208.8 in FIG.5 correspond to elements 109.1, 109.2, 117, 109.3, 108.3 and 108.8,respectively, in FIG. 3 discussed above.

The only main difference with respect to the facet mirror device 106.1lies within the design of the flexure unit 208.4. In the embodimentshown, the flexure unit 208.4 is formed by suitable generallyring-shaped slots (connected over certain parts of the circumference ofthe second support element 208.2 by radial slots) within the base body208, thereby forming a plurality of (preferably evenly distributed) leafspring elements 208.5. Elastic hinges 208.9 may be formed at at leastone end of the respective leaf spring element 208.5 to facilitateorientation adjustment. It will be appreciated that the flexure unit208.4 allows motion in two rotational degrees of freedom (namelyrotation about the x- and y-axis) while restricting motion in all otherfour degrees of freedom.

The connection between the connector element 208.7 and the first supportelement 208.1 and the second support element 208.2 is made in a sealingmanner such that a cavity 218 at the rear side of the base body 208 maybe filled with a cooling medium while the space surrounding the facetelements 209 is evacuated.

In the foregoing, the invention has been described in the context ofembodiments where the optical module according to the invention is usedin the illumination unit. However, it will be appreciated that theoptical module according to the invention may provide its beneficialeffects as well in the optical projection unit.

In the foregoing, the invention has been described in the context ofembodiments working in the EUV range. However, it will be appreciatedthat the invention may also be used at any other wavelength of theexposure light, e.g. in systems working at 193 nm etc.

Finally, in the foregoing, the invention has been described solely inthe context of microlithography systems. However, it will be appreciatedthat the invention may also be used in the context of any other opticaldevice using facet mirror devices.

What is claimed is:
 1. A facet mirror device, comprising: a facetelement; and a support unit, comprising: a first support element; asecond support element; a flexure unit comprising flexure; and aconnector element, wherein: the second support element is connected tothe facet element to support the facet element; the first supportelement is connected to the second support element to support the secondsupport element; the first support element is connected to the secondsupport element via the flexure unit; the first support element isbetween the flexure unit and the connector element; the flexure unit isbetween the first and second support elements; and the first supportelement is connected to the second support element via the connector. 2.The facet mirror device of claim 1, wherein at least one of thefollowing holds: the flexure unit defines a guiding unit configured toguide the facet element in an adjustment motion; the flexure unitrestricts relative motion between the first and second support elementsin at least two degrees of freedom; the flexure unit restricts relativemotion between the first and second support elements in exactly threedegrees of freedom; and the flexure unit restricts relative motionbetween the first and second supports element in two translationaldegrees of freedom and one rotational degree of freedom.
 3. The facetmirror device of claim 1, wherein the flexure unit restricts relativemotion between the first and second support elements in twotranslational degrees of freedom, and the flexure unit comprises aflexure element mainly extending in a plane defined by the twotranslational degrees of freedom.
 4. The facet mirror device of claim 1,wherein the flexure unit comprises at least one member selected from thegroup consisting of an elastic hinge element, a leaf spring element, anda membrane element.
 5. The facet mirror device of claim 1, wherein atleast one of the following holds: the flexure unit is monolithic withthe first support element; and the flexure unit is monolithic with thesecond support element.
 6. The facet mirror device of claim 1, whereinthe second support element extends within a recess of the first supportelement.
 7. The facet mirror device of claim 1, further comprising anadjustment device, wherein: the second support element has an adjustmentinterface configured to be contacted by the adjustment device; and atleast one of the following holds: the adjustment device is configured toadjust a relative position between the facet element and the supportunit; and the adjustment device is configured to adjust a relativeorientation between the facet element and the support unit.
 8. The facetmirror device of claim 1, wherein the first and second support elementsare connected together at an interface so that, during operation of thefacet mirror device, fluid leakage through the interface between thefirst and second support elements is prevented.
 9. The facet mirrordevice of claim 1, wherein the second support element extends through anopening within the support element, and the connector element is locatedat a rear side of the first support element facing away from the facetelement.
 10. The facet mirror device of claim 1, wherein the connectorelement is connected via an adhesive bond to at least one memberselected from the group consisting of the first support element and thesecond support element.
 11. The facet mirror device of claim 1, whereinthe connector element is bonded to at least one member selected from thegroup consisting of the first support element and the second supportelement.
 12. The facet mirror device of claim 1, wherein at least one ofthe following holds: the connector is glued to at least one memberselected from the group consisting of the first support element and thesecond support element; the connector is soldered to at least one memberselected from the group consisting of the first support element and thesecond support element; the connector is laser welded to at least onemember selected from the group consisting of the first support elementand the second support element; and the connector is diffusion bonded toat least one member selected from the group consisting of the firstsupport element and the second support element.
 13. The facet mirrordevice of claim 1, wherein at least one of the following holds: thesupport unit comprises a cooling duct configured to receive a coolingmedium during operation of the facet mirror device; and a cooling cavityis disposed at a rear side of the first support element facing away fromthe facet element, and the cooling cavity is configured to be filledwith a cooling medium.
 14. The facet mirror device according to claim 1,wherein at least one of the following holds: the support unit comprisesa plurality of support sections, and each support section is connectedto the first support element and supporting a further facet element; andthe support unit supports at least 1000 facet elements.
 15. The facetmirror device of claim 1, further comprising an adjustment device,wherein the second support element extends through an opening within thefirst support element, and an adjustment interface for the adjustmentdevice is formed at a rear end of the second support element facing awayfrom the facet element.
 16. The facet mirror device of claim 15,wherein: the second support element has an adjustment interfaceconfigured to be contacted by the adjustment device; and at least one ofthe following holds: the adjustment device is configured to adjust arelative position between the facet element and the support unit; andthe adjustment device is configured to adjust a relative orientationbetween the facet element and the support unit.
 17. The facet mirrordevice of claim 1, wherein the facet mirror device comprises a pluralityof facet elements.
 18. An optical imaging arrangement, comprising: anillumination unit configured to illuminate an object in a first plane;and an optical projection unit configured to transfer an image of thepattern onto a second plane, wherein: at least one unit selected fromthe group consisting of the illumination unit and the optical projectionunit comprises a facet mirror device; and the facet mirror devicecomprises: a facet element; and a support unit comprising first andsecond support elements; a flexure unit comprising a flexure; and aconnector element; the second support element is connected to the facetelement to support the facet element; the first support element isconnected to the second support element to support the second supportelement; the first support element is connected to said the supportelement via the flexure unit; the first support element is between theflexure unit and the connector element; the flexure unit is between thefirst and second support elements; and the first support element isconnected to the second support element via the connector element. 19.The optical imaging arrangement of claim 18, wherein the illuminationunit comprises the facet mirror device.
 20. The optical imagingarrangement of claim 18, wherein at least one of the following holds:the flexure unit defines a guiding unit configured to guide the facetelement in an adjustment motion; the flexure unit restricts relativemotion between the first and second support elements in at least twodegrees of freedom; the flexure unit restricts relative motion betweenthe first and said second support elements in exactly three degrees offreedom; and the flexure unit restricts relative motion between thefirst and second supports element in two translational degrees offreedom and one rotational degree of freedom.
 21. The optical imagingarrangement of claim 18, wherein the facet mirror device comprises aplurality of facet elements.
 22. A method, comprising: supporting afacet element of a facet mirror device via a support unit, the supportunit comprising first support and second support elements, the secondsupport element being connected to the facet element to support thefacet element, the first support element being connected to the secondsupport element to support the second support element, the first supportelement being connected to the second support element via a flexureunit, the flexure unit comprising a flexure, the first support elementbeing between the flexure unit and the connector element, the flexureunit being between the first and second support elements, and the firstsupport element being connected to the second support element via aconnector element which is separate from the flexure unit.
 23. Themethod of claim 22, further comprising at least one of the following:during operation of the facet mirror device, performing at least one ofthe following: adjusting a position of the facet element with respect tothe support unit according to optical needs; and adjusting anorientation of the facet element with respect to the support unitaccording to optical needs; using an adjustment device which contacts anadjustment interface of the second support element to adjust at leastone of the following: the position of the facet element with respect tothe support unit; and the orientation of the facet element with respectto the support unit; and using the flexure unit to guide the facetelement in an adjustment motion to adjust at least one of the following:the position of the facet element with respect to the support unit; andthe orientation of the facet element with respect to the support unit.24. The method of claim 22, further comprising at least one of thefollowing: fixing the facet element to the support unit; and connectingthe first and second support elements at an interface so that, duringoperation of the facet mirror device, fluid leakage through theinterface between the first and second support elements is prevented.25. The method of claim 22, wherein the facet mirror device comprises aplurality of facet elements.
 26. A facet mirror device, comprising: afacet element; and a support unit, comprising: a first support element;a second support element; a flexure unit comprising a flexure; and aconnector element, wherein: the second support element is connected tothe facet element to support the facet element; the first supportelement is connected to the second support element to support the secondsupport element; the first support element is connected to the secondsupport element via the flexure unit; the first support element isconnected to the second support element via the connector element; andthe flexure unit and the connector element are arranged kinematically inparallel between the first support element and the facet element. 27.The facet mirror device of claim 26, wherein the facet mirror devicecomprises a plurality of facet elements.
 28. A facet mirror device,comprising: a facet element; a support unit, comprising: a first supportelement; a second support element; a flexure unit comprising flexure;and a connector element, and an adjustment device; wherein: the secondsupport element is connected to the facet element to support the facetelement; the first support element is connected to the second supportelement to support the second support element; the first support elementis connected to the second support element via the flexure unit; thefirst support element is connected to the second support element via theconnector; the flexure unit is in direct contact with both the firstsupport element and the second support element; and wherein at least oneof the following holds: the second support element has an adjustmentinterface configured to be contacted by the adjustment device, and theadjustment device is configured to adjust at least one of the following:a relative position between the facet element and the support unit; anda relative orientation between the facet element and the support unit;and the second support element extends through an opening within thefirst support element, and an adjustment interface for the adjustmentdevice is formed at a rear end of the second support element facing awayfrom the facet element.
 29. The facet mirror device of claim 28, whereinthe facet mirror device comprises a plurality of facet elements.